1. Field of Invention
This invention relates generally to toilet flushers, specifically to an improved dual-mode, or dual-volume, water-conserving flushing mechanism.
2. Prior Art
Household tank toilets are flushed by opening a flap valve at the bottom of the water tank to release the stored water, usually 19 liters (5 gallons), into the toilet bowl. Household flush-valve toilets use a delay-closing valve and a high-capacity supply pipe to rapidly deliver a similar quantity of water into the bowl. In either case the water carries the waste matter over a weir and out of the bowl, through a bowl trap, and into the sewer pipe by gravity and siphonic action. The siphonic action, when combined with gravity, causes the water to empty very rapidly, thereby carrying away all of the waste matter in the bowl. Initiating the siphonic action requires sufficient starting amounts of water in the bowl and the water tank. If either the bowl or the tank contain insufficient amounts of water, the siphon effect cannot be achieved and the bowl will not flush properly, allowing some waste matter to be left in the bowl.
Water used in flushing toilets accounts for a significant portion of water usage in most households. As stated, a typical toilet uses about 19 liters per flush. Solid wastes require the full capacity of the tank or flush valve to be flushed away. But liquid waste can be flushed with as little as 3.8 liters (1 gallon) from the tank if the bowl contains a sufficient starting amount of water, which is about 5.7 liters (1.5 gallons). Therefore, many different "dual mode" flushing mechanisms, or flushers, have been designed to provide two selectable flushing capacities, one for each type of waste. These dual mode, or dual flush, toilets can potentially save significant amounts of water by minimizing the water used for flushing liquid wastes.
A toilet bowl needs to be fully refilled after a flush so that it will flush properly the next time. A conventional fill valve in the tank usually accomplishes this by diverting, or bleeding, a small amount of water into the bowl through an overflow pipe during the refilling of the water tank. The fill valve has a fixed bleed rate designed so that the bowl will be fully refilled in the time it takes to fully refill the tank. However, after a toilet is flushed with a small amount of water, or small flush, the tank is refilled too quickly to allow the bowl to be fully refilled. The insufficiently filled bowl will not flush the next time, but will instead be filled to capacity by the discharged water from the tank. An additional flush is then needed to clear the dirty bowl. As a result, water is wasted. Many dual mode flushers suffer from this fault, including those of U.S. Pat. Nos. 5,075,907 to Harris (1991), 4,881,279 to Harney (1989), 4,864,665 to Toltzman (1989), and 4,837,867 to Miller (1989).
The dual-mode flusher shown in U.S. Pat. No. 4,504,984 to Burns (1985) can achieve a complete flush after a small flush. It accomplishes this by using an inefficiently large amount of water, which is not user adjustable, for the small flush so as to leave a larger amount of water in the bowl after the flush. Combined with the relatively large amount of water released from the tank in the next small flush, a complete flush can be achieved. However, maximum possible water conservation cannot be achieved with this design. U.S. Pat. Nos. 4,748,699 to Stevens (1988) and 4,134,165 to Phripp et al. (1979) show flushers which allow the user to adjust the volume of the small flush. However, the volume of the small flush cannot be adjusted below a still relatively large amount if complete and reliable flushes are to be guaranteed.
In summary, existing dual mode flushers have no means to refill the toilet bowl fully after a small flush. Therefore, they either require an additional flush after each small flush to clear the bowl, or they sacrifice efficiency for reliability by using large amounts of water for the "small" flush to ensure complete flushes every time.